Process of treating waste liquors from soda-pulp mills.



L E. L. RINMAN. PROCESS OF TREATING WASTE LIQUORS FROM SODA PULP MILLS.APPLICATION FILED APRJO, 1909.

1,005,882. Patented Oct. 17,1911.

witneww' fruz-e tar the said process the liquor is freed from-the UNI EDsfr TEs PATENT. OFFICE,"

ERIK LUDVIG RINMA N, OFGOTTENBORG, SWED EN."

r'nocass or TREATING WASTE mouons'rnom sonA-ruLr m nts.

, K a v a Application filed April 10, 1909. Serial No. 489,168.

To all whom it may concern:

Be it known that'L-ERL LUDVIG RINMAN,

a subject of the King of Sweden, and resident of Gottenborg, in theKingdom of Sweden, have invented new and useful Imv in his patentspecification No. 132452 in' what manner the organic substances of ablack liquor may be recipitated by carbonic acid and utilized. owever,such a precipitatlon of the organic substances could not be performedotherwise than so as to cause a great quantity of soda to beprecipitated with the saidsubstances.

On account of the soda thus precipitated being lost, the process has notbeen practically available. In

order that the regeneration of a black liquor shall be-economical, it isnecessary that by organic substances without too great a loss of sodaarisingi 1 The object of the present invention is to provide a "processaccording to which the precipitation of the organic substances by meansof carbonic acid is performed'with a minimum loss of soda.

The invention consists, chiefly, in that the treatment of the wasteliquors with carbonic erformed in the presence of such.

acidis a quant ty o k li compounds (salts and hydrates) soluble in .thesaid liquor that a concentration is obtained which may be recognized bythefa'ct-that, it the precipitation with carbonic acid is performed ator about 75 centigrade, the ulmous substances (ulmic compounds) areobtained in a finegrained or crystalline form. By this method theprecipitate will be obtained in an easily filterable and easily washableform. The process may be employed whether the liquor contains sulfurousorganic compounds or not, and it may be carried out at ordinarytemperature or, preferably, at a raised temperat uaea as hereinafter-more particularly described. The desired concentration of the solublealkali compounds (salts and hydrates) may "be obtained by evaporation,by adding salts or hydrates soluble in the said liquor, or by acombination of these means.

In order that my invention may be more easlly understood, I will nowproceed to more fully describe thenature of the invengeously be carriedinto efl'ect.

An examination of the organic compounds which are formed when cellulosematerials are boiled with caustic soda proves that the Specification .5:Letters Patent. Patented 0017117, 1911.

tion and in what-manner it may 'advantasaid compounds may be divided intwo groups, apart from all regard to substances which are'c'ertainlyformed in boiling cellulose but which may be separated from the liquoron account of their property of being volatile or because they distilover with water, such as turpentine; methyl alcohol,

(mercaptans, sulfids), ammonia, etc. One

less acid character than carbonic acid -whereas the other-group has amore acid character. For the sake of simplicity, the first type oforganic substances are herein.-

type'being called organic acids.

Therul'mous substances form the bulk'of the organic compounds foulingthe black liquors, from fir-wood about 30 per cent. of

the weightof the absolutely dry wood. Re-

of the said main groups of organic com-. pounds is recognized by thesame having a after called ulmous substances, the. other garding theirproperties the following is to be noted. They are colloidally' solublein water which has been made weakly allralinei by carbonate of soda butare prec1p1tated from such a water solution if a sufliclent.

quantity of. alkali salts is added. i They are diflicult to dissolve incold water, easier in warm water. When precipitated *from a warmsolution, they are obtained in a form which is more diflicultto'dissolve than that obtained when they are precipitated from asolution of ordinary temperature They-are easily dissolved in alkalineliquids, more diflicult in liquids of weak alkalinity, such .as wateralkalized by carbonate of soda. Their sodium salts are decomposed byacids,

even by so weak an acid as carbonic acid.

On account of these properties of the ulmous substances, it is obviousthat they cannot be preci ita ted in a filterable form by carbonic acidrom their sodium salts in a black liquor without certain measures beingtaken.

I will now describe in what manner a satisfactory precipitation may beobtained.

In order that the ulmous substances freed by carbonic acid from theirsodium salts shall be precipitated, the black liquor must have a certainconcentration of alkali salts soluble therein. It is obviousthat-precipitating salts are formed when carbonic acid bedirectly'precipitated by carbonic acid in.

a filterable form. Generally, however, di-

. lute black liquors are obtained, which must be reduced by evaporationto a suitable concentration. By evaporating the liquor before, during,or after the precipitation with carbonic acid, obviously such a saltconcentration of carbonate of soda of any strength up to saturatedsolution is obtained. However, in order to obtain this result a strongevaporation is required which would be for economical and other reasonsdisadvantageous. y

In order, under all circumstances, to obtain a sufficient concentrationof salts soluble in the liquid, it is preferred to add to the liquor asuflicient quantity of one or more inorganic alkali salts solubletherein, since the presence of such salts considerably increases theeffect. in precipitating the ulmous substances without preventing theemployment of the lye for boiling cellulose matters. Among the saltswhich may be used potassic and soda-salts and, further, ammoniumcarbonate may be mentioned. The potassic salts are inappropriate onaccount of their high price. Among the sodium salts only the sulfate,the carbonate and the chlorid may, preferably, be used. Among the saltsmentioned the sodium sulfate is very active but it gives rise tosulfurous lyes if the lime used in causticizing is reburned for repeateduse or if, on any occasion, the lyes are regenerated by calcination.Sodium carbonate may, obviously, be employed, but a better result isobtained by using sodium chlorid which is more active and also cheaperthan sodium carbonate.

If a black liquor is. completely saturated with sodium chlorid oranother inorganic sodium salt, the ulmous substances are practicallycompletely precipitated if carbonicv In practice, it is,

acid is led into the liquor. however, not necessary to add such aquanciently active. In precipitating the ulmous substances, by means ofcarbonic acid, from a black liquor, a suflicient preclpitatlon'lsobtained, for instance in boiling fir-wood, if

the liquor during or after theprecipitation has a concentration of about100 gr. of Na O and 50 gr. of N aCl per liter of liquor (about 20 B.)- 7

As the ulmous substances precipitated in a cold solution are easilysoluble in water which, however, is not the case when they areprecipitated in a warm solution it is ob vious that, in order that theymay be washable without too great a loss, said substances should eitherbe' precipitated from a warm solution or be warmed during or after theprecipitation so as to become diflicult to dissolve. It thereby appearsthat the ulmous substances obtain a grainy form if they are heated,after the precipitatiomto about centigrade, and particularly they {areobtained in a very fine-grained or micro-crystalline form if the liquorduringvthe pre cipitation has a temperature of about 75 centigrade. Ifthe ulmous substances are heated to temperatures above 85 centigradethey are very liable to cake and melt. Even at a temperature of about 75centigrade they may cake, if subjected to pres-' sure. If it is desiredto maintain them in a filterable form, they should, therefore, at

this temperature be kept in motion in the liquor and be cooled beforefiltration, since, if they are cooled to ordinary temperature, they donot cake but filter and are very easily washed. Ulmous substancesprecipitated in a filterable form lose this pro erty if they are exposedfor a long time some days orweeks according to whether the liquor iskept in motion or not) to a solution of sodium carbonate. On accountthereof, precipitated ulmous substances which are to be filteredshould'beseparated from the mother-liquor without delay. By heating andsubsequent cooling, ulmous substances which cannot be filtered are againmade filterable.

In order that the ulmous substances may be precipitated from a blackliquor at about 75 centigrade in a "fine-grained or or stalline form,the liquor must have a su cient concentration of salts soluble therein;if this is not the case, neither a substantially complete precipitationnor a fine-grained, easily filterable product is obtained. Too" great aconcentration of ulmous substances makes the preci itate so extremelyfine-grained that it Wlll be difiicult to filter and wash. In order toavoid this, the liquor may be concentrated partly by evaporation andpartly by adding alkali salts, preferably salts with strong acids, sincesuch salts are more active than other salts.

a It should noted that too high a concen .tration of ulmous substancesis unfavorable no maximum concentration of inbefore described'maybeused, after causticizing, for boiling fresh quantities of cellulosematters. Hereby, obviously, care must be taken that the liquor containsa sufiicient concentration of Na O. The dissolving of I salts in theliquor has no disadvantagesbut,

on the contrary, a favorable influence, in that, particularly in thepresence of sodium chlorid, a more easily bleached and stronger fiber isobtained; One and the same-liquor,

treated each time in the. manner 'hereinbefore described, may be usedwithout inbolling further quantities of cellulose mat-' convenienceseveral times for boiling cellulose matters since the increase in thequantity of organic acids (chieflyresinous acids, formic acid and aceticacid) is not so eat that the said acids will have any disa vantageou'sinfluence when the liquor is used for ters. In the re neration of thelye by means of carbonic acid the organic acids serve as precipitatingsalts, and on account thereof the quantity of inorganic precipitatingsalts maybe reduced. In practice, it

is therefore only'ynecessary that. for each boiling a fraction of theliquor previously employed is replaced by-fr'esh lye of suitablecomposition. The liquor removedmay, if

desired, be treated for recovering sodium carbonate or said salt andother salts.

A satisfactory recipitation of the ulmous substances of a lack liquor bymeans of carbonic acid is also obtained if the precipitation takes placein the presence of ammonium carbonate as a precipitating salt. However,this procedure ms the drawback that greater care is required duringwork'- ing, in order to avoid loss of ammonia. On

the other hand, it has the advantage thatthe carbonate of ammonia may beeasily separated from the liquor, by known methods, after the ulmoussubstances have been separated, so that in boiling the. cellulose rawmaterial. asoda-lye of awell known eflicacy may be employed. Moreover,the

ulmous substances may thereby be easily freed from mother-liquor andfrom washwater that may contain carbonate of ammonia. Addition of otherammonium salts has, obviously, no other influence than the addition ofthe corresponding sodium salt and carbonate of ammonia;

In the accompanying drawing, I have :shown, inside-elevation and part alsecrying m invention into effect. It is, however, to noted that I do notlimit myself to any specific apparatus since any a paployed. I

Referring to the drawing, the hot black liquor having a suitableconcentration and temperature (about cent ade) is led ,'through tubes 1into one or t e other of a series .of receptacles 2, 2. Then carbonicacid gas is led through a tube 3 into the tained consisting chiefly, of.ulmous sub stances, as hereinbefore described. It is not necessary touse pure'carbonic acid gas, but in order to reduce the costs, chimneygases coolers 8 and thence through-a tube 9.to the $12 to a vacuumapparatus" (not shown).

and caused by apump 14. to pass through the coolers 8 1n a directionopposite to that of the liquor from the receptacles 2, b

grade. From the coolers 8 a tube 15 leads to the mixers 16 where theliquor is causticized by lime in usual manner.

All additions to the liquor of sodium chlorid, soda, and the like,vshould, preferably, be made before causticizing so that disagreeableimpurities may be precipitated.

If the ulmous substances are precipitated in a cold solution which isthereupon heated for transforming the said substancesinto a more easilyfilterable and washable form, they cannot be so easily nor so completelyfreed from the mother-liquor, whereforethis procedure is not 'soadvantageous as when centigrade.

In precipitating the black liquor by means of carbonic acid, the methodof sprinklmg the liquor in the form of a fine spray, for instance by anatomizer or a centrifugal liqentai any advantage, as compared with themethod of precipitating at a temperature" of about 75 centigrade.

It is remarked that hydrochloric acid, and subsequent washing blackliquor, whereby a precipitate is ob- (containing about 10 per cent. ofcarbonic The filtrate is drawn off through a cock .13-

the precipitation is effected at about 75 uid s reader, into carbonicacid gas does not.

- tion, a system of apparatus adapted for carratus suitable for thepurpose may be eminis caused-to pass t rough a tubeZ to the I I, A

filtering apparatus 10 in Which the space beneath the filter 11 isconnected by a tube which it is again heated to about 75 centiby washingthe ulmous substances with a strong acid, for mstance .130

with water'a product is obtained which is almost chemically free fromash. Ulmous substances, washed with water and thereupon acidified may beeasily freed from their percentage of mother-liquor by heating underpressure to temperatures between 120 to 200 centigrade. The organicsubstance melts toa resinous mass while the mother-liquor is separatedas such.

I claim:

1. The method of precipitating, in a fil terable form, the ulmoussubstances contained in the waste liquors from soda pulp mills, whichconsists in treating said liquors at a concentration of about B., and ata temperature of about 75 0., with carbon dioxid, substantially as andfor the purpose set forth.

2. The method of precipitating, in a filterable form, the ulmoussubstances contained in the waste liquors from soda pulp mills, whichconsists in treating said liquors with carbon dioxid, in presence of analkali than carbonic acid; substantially as and for the purpose setforth;

4. The method of precipitating, in a filterable form, the ulmoussubstances contained in the waste liquors from soda pulp mills, whichconsists in treating saidrliquors with carbon dioxid, in presence ofsodium chlorid, substantially as and for the purpose set forth.

ERIK LUDVIG RINMAN.

lVitnesses AUG. SoRENsEN, KARL RUN OSKOG.

